mirror of https://github.com/mkerrisk/man-pages
Further substantial rewrites.
This commit is contained in:
Michael Kerrisk
parent
d77067bde1
commit
a62f51211f
149
man2/mmap.2
149
man2/mmap.2
|
|
@ -1,6 +1,7 @@
|
|||
.\" Hey Emacs! This file is -*- nroff -*- source.
|
||||
.\"
|
||||
.\" Copyright (C) 1996 Andries Brouwer (aeb@cwi.nl)
|
||||
.\" Copyright (C) 1996 Andries Brouwer <aeb@cwi.nl>
|
||||
.\" and Copyright (C) 2006 Michael Kerrisk <mtk-manpages@gmx.net>
|
||||
.\"
|
||||
.\" Permission is granted to make and distribute verbatim copies of this
|
||||
.\" manual provided the copyright notice and this permission notice are
|
||||
|
|
@ -32,15 +33,17 @@
|
|||
.\" Modified 2004-09-11 by aeb
|
||||
.\" Modified 2004-12-08, from Eric Estievenart <eric.estievenart@free.fr>
|
||||
.\" Modified 2004-12-08, mtk, formatting tidy-ups
|
||||
.\" Modified 2006-12-04, mtk, various parts rewritten
|
||||
.\"
|
||||
.TH MMAP 2 2004-12-08 "Linux 2.6.9" "Linux Programmer's Manual"
|
||||
.TH MMAP 2 2006-12-04 "Linux 2.6.19" "Linux Programmer's Manual"
|
||||
.SH NAME
|
||||
mmap, munmap \- map or unmap files or devices into memory
|
||||
.SH SYNOPSIS
|
||||
.nf
|
||||
.B #include <sys/mman.h>
|
||||
.sp
|
||||
.BI "void *mmap(void *" start ", size_t " length ", int " prot ", int " flags ,
|
||||
.BI "void *mmap(void *" start ", size_t " length \
|
||||
", int " prot ", int " flags ,
|
||||
.BI " int " fd ", off_t " offset );
|
||||
.sp
|
||||
.BI "int munmap(void *" start ", size_t " length );
|
||||
|
|
@ -75,6 +78,9 @@ bytes starting at offset
|
|||
.I offset
|
||||
in the file (or other object) referred to by the file descriptor
|
||||
.IR fd .
|
||||
.I offset
|
||||
must be a multiple of the page size as returned by
|
||||
.IR sysconf(_SC_PAGE_SIZE) .
|
||||
.LP
|
||||
The
|
||||
.I prot
|
||||
|
|
@ -82,7 +88,7 @@ argument describes the desired memory protection of the mapping
|
|||
(and must not conflict with the open mode of the file).
|
||||
It is either
|
||||
.B PROT_NONE
|
||||
or is the bitwise OR of one or more of the following flags:
|
||||
or the bitwise OR of one or more of the following flags:
|
||||
.TP 1.1i
|
||||
.B PROT_EXEC
|
||||
Pages may be executed.
|
||||
|
|
@ -98,14 +104,44 @@ Pages may not be accessed.
|
|||
.LP
|
||||
The
|
||||
.I flags
|
||||
parameter specifies the type of the mapped object, mapping options and
|
||||
whether modifications made to the mapped copy of the page are private to
|
||||
the process or are to be shared with other references.
|
||||
The following values can be ORed in
|
||||
argument determines whether updates to the mapping
|
||||
are visible to other processes mapping the same region,
|
||||
and whether updates are caried through to the underlying file.
|
||||
This behaviour is determined by including exactly one
|
||||
of the following values in
|
||||
.IR flags :
|
||||
.TP 1.1i
|
||||
.B MAP_SHARED
|
||||
Share this mapping.
|
||||
Updates to the mapping are visible to other processes that map this file,
|
||||
and are carried through to the underlying file.
|
||||
The file may not actually be updated until
|
||||
.BR msync (2)
|
||||
or
|
||||
.BR munmap (2)
|
||||
is called.
|
||||
.TP
|
||||
.B MAP_PRIVATE
|
||||
Create a private copy-on-write mapping.
|
||||
Updates to the mapping are not visible to other processes
|
||||
mapping the same file, and are not carried through to
|
||||
the underlying file.
|
||||
It is unspecified whether changes made to the file after the
|
||||
.BR mmap ()
|
||||
call are visible in the mapped region.
|
||||
.LP
|
||||
Both of these flags are described in POSIX.1-2001.
|
||||
|
||||
In addition, zero or more of the following values can be ORed in
|
||||
.IR flags :
|
||||
.\" FIXME ? Place the following list in alphabetical order?
|
||||
.TP
|
||||
.B MAP_FIXED
|
||||
Do not select a different address than the one specified.
|
||||
Don't interpret
|
||||
.I start
|
||||
as a hint: place the mapping at exactly that address.
|
||||
.I start
|
||||
must be a multiple of the page size.
|
||||
If the memory region specified by
|
||||
.I start
|
||||
and
|
||||
|
|
@ -115,37 +151,8 @@ part of the existing mapping(s) will be discarded.
|
|||
If the specified address cannot be used,
|
||||
.BR mmap ()
|
||||
will fail.
|
||||
If
|
||||
.B MAP_FIXED
|
||||
is specified,
|
||||
.I start
|
||||
must be a multiple of the page size.
|
||||
Use of this option is discouraged.
|
||||
.TP
|
||||
.B MAP_SHARED
|
||||
Share this mapping with all other processes that map this object.
|
||||
Storing to the region is equivalent to writing to the file.
|
||||
The file may not actually be updated until
|
||||
.BR msync (2)
|
||||
or
|
||||
.BR munmap (2)
|
||||
are called.
|
||||
.TP
|
||||
.B MAP_PRIVATE
|
||||
Create a private copy-on-write mapping.
|
||||
Stores to the region do not affect the original file.
|
||||
It is unspecified whether changes made to the file after the
|
||||
.BR mmap ()
|
||||
call are visible in the mapped region.
|
||||
.LP
|
||||
You must specify exactly one of
|
||||
.B MAP_SHARED
|
||||
and
|
||||
.BR MAP_PRIVATE .
|
||||
.LP
|
||||
The above three flags are described in POSIX.1-2001.
|
||||
Linux also knows about the following non-standard flags:
|
||||
.\" FIXME ? Place the following list in alphabetical order?
|
||||
Because requiring a fixed address for a mapping is less portable,
|
||||
the use of this option is discouraged.
|
||||
.TP
|
||||
.B MAP_DENYWRITE
|
||||
This flag is ignored.
|
||||
|
|
@ -183,9 +190,15 @@ This flag is ignored in older kernels.
|
|||
.\" If set, the mapped pages will not be swapped out.
|
||||
.TP
|
||||
.B MAP_GROWSDOWN
|
||||
Used for stacks. Indicates to the kernel VM system that the mapping
|
||||
Used for stacks.
|
||||
Indicates to the kernel virtual memory system that the mapping
|
||||
should extend downwards in memory.
|
||||
.TP
|
||||
.B MAP_ANON
|
||||
Synonym for
|
||||
.BR MAP_ANONYMOUS .
|
||||
Deprecated.
|
||||
.TP
|
||||
.B MAP_ANONYMOUS
|
||||
The mapping is not backed by any file;
|
||||
its contents are initialised to zero.
|
||||
|
|
@ -193,16 +206,21 @@ The
|
|||
.I fd
|
||||
and
|
||||
.I offset
|
||||
arguments are ignored.
|
||||
The use of this flag in conjunction with
|
||||
arguments are ignored;
|
||||
however, some implementations require
|
||||
.I fd
|
||||
to be \-1 if
|
||||
.B MAP_ANONYMOUS
|
||||
(or
|
||||
.BR MAP_ANON )
|
||||
is specified,
|
||||
and portable applications should ensure this.
|
||||
The use of
|
||||
.B MAP_ANONYMOUS
|
||||
in conjunction with
|
||||
.B MAP_SHARED
|
||||
is only supported on Linux since kernel 2.4.
|
||||
.TP
|
||||
.B MAP_ANON
|
||||
Synonym for
|
||||
.BR MAP_ANONYMOUS .
|
||||
Deprecated.
|
||||
.TP
|
||||
.B MAP_FILE
|
||||
Compatibility flag. Ignored.
|
||||
.TP
|
||||
|
|
@ -225,31 +243,17 @@ Don't perform read-ahead:
|
|||
only create page tables entries for pages
|
||||
that are already present in RAM.
|
||||
.LP
|
||||
Of the above flags, only
|
||||
.B MAP_FIXED
|
||||
is specified in POSIX.1-2001.
|
||||
However, most systems also support
|
||||
.B MAP_ANONYMOUS
|
||||
(or its synonym
|
||||
.BR MAP_ANON ).
|
||||
.LP
|
||||
Some systems document the additional flags MAP_AUTOGROW, MAP_AUTORESRV,
|
||||
MAP_COPY, and MAP_LOCAL.
|
||||
.LP
|
||||
.I fd
|
||||
should be a valid file descriptor, unless
|
||||
.B MAP_ANONYMOUS
|
||||
is set.
|
||||
If
|
||||
.B MAP_ANONYMOUS
|
||||
is set, then
|
||||
.I fd
|
||||
is ignored on Linux.
|
||||
However, some implementations require
|
||||
.I fd
|
||||
to be \-1 if
|
||||
.B MAP_ANONYMOUS
|
||||
(or
|
||||
.BR MAP_ANON )
|
||||
is specified,
|
||||
and portable applications should ensure this.
|
||||
.LP
|
||||
.I offset
|
||||
should be a multiple of the page size as returned by
|
||||
.BR getpagesize (2).
|
||||
.LP
|
||||
Memory mapped by
|
||||
.BR mmap ()
|
||||
is preserved across
|
||||
|
|
@ -320,9 +324,10 @@ is set (probably to
|
|||
.SH NOTES
|
||||
It is architecture dependent whether
|
||||
.B PROT_READ
|
||||
includes
|
||||
implies
|
||||
.B PROT_EXEC
|
||||
or not. Portable programs should always set
|
||||
or not.
|
||||
Portable programs should always set
|
||||
.B PROT_EXEC
|
||||
if they intend to execute code in the new mapping.
|
||||
.SH ERRORS
|
||||
|
|
|
|||
Loading…
Reference in New Issue